added PR base branch

Author: mtrezza

.github/workflows/ci.yml

@@ -39,6 +39,7 @@ jobs:
           body: This is an automated PR to upgrade package versions in CI environments for MongoDB, Node.js.
           commit-message: Upgrading versions of MongoDB / Node.js
           branch: ci/upgrade-ci-environments
+          base: master
   check-lint:
     name: Lint
     timeout-minutes: 30